there waterproof to a point, putting it in the water that deep should be ok. But if you pushed truck further down the pressure of the water would easily go in,Just like watches that say waterproof to 100m and others say waterproof to 1000m. you can wear both watches in the swimming pool but the further you take it down the more pressure is put onto it by the weight of the water.
They say water resistant because they don't want you to do the swimming thing.
some break going through puddles, some can drive below the water level.Even though it's the exact same model. it's normally measured as an IP rating in uk. the higher the number the more water resistant it is.
Or using a hose pipe to wash your car down a hose on little pressure should be fine a high pressure hose will damage it.